Typical refrigerant systems include a compressor that compresses gaseous refrigerant received from an evaporator. Under certain conditions, such as during startup or transient operation, refrigerant might not fully vaporize in the evaporator, and thus the refrigerant might enter the compressor as a liquid, which can damage a compressor, particularly if the compressor is a positive displacement one.
To inhibit liquid refrigerant from entering a compressor, U.S. Pat. No. 3,412,574 suggests using a float valve between the evaporator and the compressor. The proposed valve includes a ball that is free to float loosely within a housing. When the housing is flooded with liquid refrigerant, the ball floats to block off a primary refrigerant outlet of the valve. In the absence of liquid, the intent is for the ball to fall back down away from the outlet to allow gaseous refrigerant to pass more freely through the housing.
If, however, the flow rate of the gaseous refrigerant is too great for the valve of the '574 patent, the gaseous refrigerant might create a velocity pressure sufficient to blow the ball upward until the ball blocks the outlet, even without liquid refrigerant. When the ball closes the outlet under such conditions, the gaseous flow becomes restricted, which could perhaps reduce the velocity pressure to a point where the ball falls back down. This would reopen the outlet, and the gaseous flow might once again blow the ball back up to obstruct the flow. If such a cycle were to repeat, the valve might begin hammering between open and closed positions.
For the valve of the '574 patent, it is also conceivable that once gaseous refrigerant blows the ball up against the outlet, the static pressure differential applied vertically across the ball might be sufficient to hold the ball in place. This might starve the compressor of refrigerant because only a restricted amount of gaseous refrigerant would be flowing through the small bypass opening of the valve.
Although these problems could be avoided by simply limiting the maximum flow rate of gaseous refrigerant through the valve, such a solution would also limit the cooling capacity of the refrigerant system over all. Consequently, there is a need for a better way of inhibiting liquid refrigerant from entering the suction inlet of a compressor.